Shear Stress Levels Research Articles

Characterization of the competing role of surface-contact and shear stress on platelet activation in the setting of blood contacting devices.

Supraphysiological shear stress and surface-contact are recognized as driving mechanisms of platelet activation (PA) in blood contacting devices (BCDs). However, the competing role of these mechanisms in triggering thrombogenic events is poorly understood. Here, we characterized the dynamics of PA in response to the combined effect of shear stress and material exposure. Human platelets were stimulated with different levels of shear stress (500, 750, 1000 dynes/cm2) over a range of exposure times (10, 20, and 30 min) within capillary tubes made of various polymeric materials. Polyethylene (PE), polytetrafluoroethylene (PTFE), ethylene tetrafluoroethylene (ETFE), and polyether ether ketone (PEEK), used for BCDs fabrication, were investigated as compared to glass and thromboresistant Sigma™-coated glass. PA was quantified using the Platelet Activity State assay. Our results indicate that mechanical stimulation and polymer surface-contact both significantly contribute to PA. Notably, the contribution of the mechanical stimulus ranges between +36% and +43%, while that associated with polymer surface-contact ranges from +48% to +59%, depending on the exposure time. In more detail, our results indicate that: (i) PA increases with increasing shear stress magnitude; (ii) PA has a non-linear, time-dependent relationship to exposure time; (iii) PA is largely influenced by biomaterials, with PE and PEEK having respectively the lowest and highest prothrombotic potential; (iv) the effects of polymer surface-contact and shear stress are not correlated and can be studied separately. Our results suggest the importance of incorporating the evaluation of platelet activation driven by the combined effect of shear stress and polymer surface-contact for the comprehensive assessment, and eventually minimization, of BCDs thrombogenic potential.

A Stochastic Model Based on Fiber Breakage and Matrix Creep for the Stress-Rupture Failure of Unidirectional Continuous Fiber Composites 2. Non-linear Matrix Creep Effects

Stress rupture (sometimes called creep-rupture) is a time-dependent failure mode occurring in unidirectional fiber composites under high tensile loads sustained over long times (e. g., many years), resulting in highly variable lifetimes and where failure has catastrophic consequences. Stress-rupture is of particular concern in such structures as composite overwrapped pressure vessels (COPVs), tension members in infrastructure applications (suspended roofs, post-tensioned bridge cables) and high angular velocity rotors (e.g., flywheels, centrifuges, and propellers). At the micromechanical level, stress rupture begins with the failure of some individual fibers at random flaws, followed by local load-transfer to neighboring intact fibers through shear stresses in the matrix. Over time, the matrix between the fibers creeps in shear, which causes lengthening of local fiber overload zones around previous fiber breaks, resulting in even more fiber breaks, and eventually, formation clusters of fiber breaks of various sizes, one of which eventually grows to a catastrophically unstable size. Most previous models are direct extension of classic stochastic breakdown models for a single fiber, and do not reflect the micromechanical detail, particularly in terms of the creep behavior of the matrix. These models may be adequate for interpreting experimental, composite stress rupture data under a constant load in service; however, they are of highly questionable accuracy under more complex loading profiles, especially ones that initially include a brief “proof test” at a “proof load” of up to 1.5 times the chosen service load. Such models typically predict an improved reliability for proof-test survivors that is higher than the reliability without such a proof test. In our previous work relevant to carbon fiber/epoxy composite structures we showed that damage occurs in the form of a large number of fiber breaks that would not otherwise occur, and in many important circumstances the net effect is reduced reliability over time, if the proof stress is too high. The current paper continues our previous work by revising the model for matrix creep to include non-linear creep whereby power-law creep behavior occurs not only in time but also in shear stress level and with differing exponents. This model, thus, admits two additional parameters, one determining the sensitivity of shear creep rate to shear stress level, and another that acts as a threshold shear stress level reminiscent of a yield stress in the plastic limit, which the model also admits. The new model predicts very similar behavior to that seen in the previous model under linear viscoelastic behavior of the matrix, except that it allows for a threshold shear stress. This threshold allows consideration of behavior under near plastic matrix yielding or even matrix shear failure, the consequence of which is a large increase in the length-scale of load transfer around fiber breaks, and thus, a significant reduction in composite strength and increase in variability. Derivations of length-scales resulting from non-linear matrix creep are provided as Appendices in the Supplementary Material.

Numerical approach-based simulation to predict cerebrovascular shear stress in a blood-brain barrier organ-on-a-chip

Most of the compounds are impermeable to the blood-brain barrier (BBB), which poses a significant challenge in the development of therapeutics for the treatment of neurological diseases. Most of the existing in vitro BBB models are not capable of mimicking the in vivo conditions and functions. The numerical approach-based simulation model was proposed to accurately predict the in vivo level shear stress for the microfluidic BBB-on-a-chip. The in vivo level shear stress was predicted for various conditions of volume flow rates, porosities of the polycarbonate membrane of the BBB model, and dimensions of the microfluidic channel. The in vivo shear stress of the microfluidic BBB model increased with a decrease in the dimension of the microfluidic channel and a decrease in the porosity. The in vivo shear stress predicted by the optimized numerical approach-based simulation was validated within 2.17% error with the experimental in vivo level of shear stress at the porosity of 0.01% and all volume flow rates. The shear stress value, according to the volume flow rate of the microfluidic BBB chip with the optimal microfluidic channel size, was effective for the successful formation of tight junctions in primary endothelial cell culture. In this regard, the proposed method provided a standard for the development of various microfluidic organ-on-chip devices that replicate the in vivo conditions and shear stress.

Friction Laws for Saturated/Unsaturated Fatty Acid Layers

The presence or absence of unsaturation in the carbon chain of carboxylic acids was examined on the friction response of boundary films according to normal force. Friction laws were established as a function of the normal force at the nanoscale with a molecular tribometer derived from a surface force apparatus. While the shear plane is mainly composed of methyl groups in all the cases investigated, the molecular organization differs within the shear plane, as suggested by the simultaneous film thickness evolution. This gave rise to dissipation modes within the interface, resulting in a wide range of shear stress levels and dependence with contact pressure. The friction laws were discussed, highlighting the combined role of nanometric surface roughness and molecule unsaturation.Graphic Abstract Friction laws for stearic acid ( ), elaidic acid ( ), and oleic acid ( ) boundary layers and schematic diagrams of the corresponding sheared interfaces

Оцінка напружено-деформаційного стану шпинделя багатоопераційного верстата

Запропоновано комплексну процедура аналізу конструкції шпиндельного вузла модернізованого токарного верстата. Наведено конструктивна і розрахункова схеми двухопорного полого шпинделя з використанням модуля аналізу напружено-деформованого стану балок АРМ Bеam. Розглянуто поперечна згортка приводу головного руху токарного верстата і визначена просторова схема сил, що діють на шпиндель. Виконано розрахунок статичної міцності за величиною еквівалентних напружень, що виникають в конструкції шпинделя. Дана оцінка рівня дотичних напружень у поперечному перетині конструкції методом кінцевих елементів.

Theoretical Analysis on Stress and Deformation of Overburden Key Stratum in Solid Filling Coal Mining Based on the Multilayer Winkler Foundation Beam Model

Solid backfill coal mining (SBCM) is a green mining technology which can effectively alleviate the environmental problems induced by traditional coal mining techniques, such as surface subsidence, water resources loss, coal gangue occupation, and pollution. In this study, a multilayer Winkler foundation beam model for the overburden key strata is proposed, and the model with two key strata is solved. The subsidence, rotating angle, inner force, and stress of the overburden key strata are systematically analyzed under various backfill elastic modulus, mining height, and soft layer thickness. The results show that the subsidence of the key strata exhibit “basin”-shape curves, and the backfill elastic modulus, mining height, and the thickness of the soft strata have significant influences on the subsidence of the key strata. The shear stress, horizontal stress, and vertical stress of key stratum can be effectively reduced by increasing the backfill elastic modulus. The increase of mining height has little influence on the stress of key stratum that close to the coal seam (key stratum #1), but has a significant effect on the stress of key stratum that above the soft layers (key stratum #2). On the contrary, the effect of increasing soft layer thickness on the stress of key stratum is opposite to that of increasing mining height. In addition, the shear failure of key stratum #1 at mining boundary and the tensile failures on both sides of mining boundary should be preferentially considered in SBCM engineering design. Due to the low shear stress level of key stratum #2, the tensile failure on both sides of the mining boundary should be mainly considered.

Shear stress inhibits cardiac microvascular endothelial cells apoptosis to protect against myocardial ischemia reperfusion injury via YAP/miR-206/PDCD4 signaling pathway

Cardiac microvascular endothelial cells (CMECs), derived from coronary circulation microvessel, are the main barrier for the exchange of energy and nutrients between myocardium and blood. However, microvascular I/R injury is a severely neglected topic, and few strategies can reverse this pathology. In this study, we investigated the mechanism of shear stress in microvascular I/R injury, and try to elucidate the downstream signaling pathways that inhibit CMECs apoptosis to reduce I/R injury. Our results demonstrated that shear stress inhibited the apoptosis protein, increased PECAM-1 expression and eNOS phosphorylation in hypoxia reoxygenated (H/R) CMECs. The mechanism of shear stress was related to up-regulated expression of YAP, the increased number of YAP entering the nucleus by dephosphorylation, the reduced number of TUNEL positive cells, increased miR-206 and inhibited protein level of PDCD4 in CMECs. However, siRNA-mediated knockdown of YAP abolished the protective effects of shear stress on CMECs apoptosis, similar results obtained from administration with AMO-miR-206, and also prevented PDCD4 (target gene of miR-206) increasing when treatment with both AMO-miR-206 and mimics-miR-206. In vivo, restoring the blood fluid with nitroglycerin (NTG) to mimic in vitro shear stress levels, which subsequently improved cardiac function, reduced infarcted area, lowered microvascular perfusion defects. Functional investigations clearly illustrated that increased the protein expression of PECAM-1 and eNOS phosphorylation, activated YAP, strengthened miR-206 expression, and suppressed PDCD4 expression. In summary, this study confirmed that shear stress reversed CMECs apoptosis, relieved microvascular I/R injury, the mechanism of which involving through YAP/miR-206/PDCD4 signaling pathway to finally suppress myocardial I/R injury.

Damage in an aluminum alloy induced by the combined action of shear stress and environmental exposure

In this work, the damage mechanism and characteristics of the 2219-C10S aluminum alloy under the combined action of an exfoliation corrosion solution and shear stress were investigated. Simple shear specimens of the material (based on ASTM B831-14) were subjected to environmental exposure experiments under simple shear stress conditions. During testing, a small band-shaped zone of simple shear stress formed in the middle of the exposed region on the specimen surface. After the specified exposure duration in the corrosive medium, the corrosion micromorphology, crack nucleation location, and crack propagation direction were analyzed. The results demonstrated that under the combined action of the corrosion solution and shear stress, tiny pits appeared on the surface of the specimen after a certain exposure duration; the shear stress promoted slip dissolution of the material at the edge of the pit via the shear slip mechanism, resulting in the formation of microcracks from the edge of the pit along the shear stress direction. The microcracks still propagated along the grain boundary in the direction roughly parallel to the shear stress. The shear stress level had no clear effect on the average corrosion depth, but it had a substantial impact on the maximum corrosion depth. With increasing shear stress, the maximum corrosion depth markedly increased along with the risk for corrosion-induced specimen failure. On doubling the exposure duration, both the average corrosion depth and the maximum corrosion depth increased, but the growth rate for the average corrosion depth decreased and it increased for the maximum corrosion depth.

Shear performance and mechanism analysis of warp-knitted non-crimp fabric composites under combined shear and tension loading

In order to further clarify the shear mechanisms and shear-tension coupling effects of warp-knitted non-crimp fabric (NCF) composites under the combined shear and tension loading, biaxial bias extension tests with three tensile stress levels (TSLs) and four shear stress levels (SSLs) were conducted. The shear stiffness was calculated by three methods to obtain accurate variation characteristics, and the shear stiffness’s nonlinearity for the first positive loading curves was analyzed based on the shear stiffness-strain curve method. The shear deformations and mechanisms of NCF and plain-woven fabric composites were discussed. Results show that, the shear deformations and plasticity of NCF composites are mainly related to the SSL, and tend to saturate with the increasing TSL when the SSL is constant, which is probably due to shear-tension coupling effects. The shear stiffness is stress-state specific, and its stable variation characteristics could only appear for some particular TSLs. Due to different internal micro-structures, the shear stiffness variation characteristics of NCF composites are different from those of plain-woven fabric composites. The used methods and conclusions obtained can provide useful references for the determination of accurate shear properties for fabric composites, as well as the design and analysis of membrane structures.

Shear Stress Rescued the Neuronal Impairment Induced by Global Cerebral Ischemia Reperfusion via Activating PECAM-1-eNOS-NO Pathway.

Microvessel hypoperfusion following ischemic stress resulted in a decreased shear stress of brain microvascular endothelial cells (BMECs) and contributed to abnormal expression of PECAM-1 after global cerebral ischemia/reperfusion (I/R) injury. Here, we identified novel pathophysiologic and rehabilitative procedures specific to shear stress in microvascular endothelial cells in response to global cerebral I/R injury. We found that the decrease in cerebral blood flow of gerbils after global cerebral I/R injury reduces shear stress, and the abnormal change in shear stress leads to microvascular endothelial cell and neuron damage. Nevertheless, suitable high levels of shear stress contribute to rescuing the dysfunction and malformation of BMECs via regulating the PECAM-1-eNOS-NO pathway to enhance nitric oxide release, decrease the expression of caspase-3 to reduce apoptosis, and improve the shear-adaptability of endothelial cells, thereby playing a protective role in the gerbil brain.

Shear Stress and RBC-NOS Serine1177 Phosphorylation in Humans: A Dose Response.

Red blood cells (RBC) express a nitric oxide synthase isoform (RBC-NOS) that appears dependent on shear stress for Serine1177 phosphorylation. Whether this protein is equally activated by varied shears in the physiological range is less described. Here, we explored RBC-NOS Serine1177 phosphorylation in response to shear stress levels reflective of in vivo conditions. Whole blood samples were exposed to specific magnitudes of shear stress (0.5, 1.5, 4.5, 13.5 Pa) for discrete exposure times (1, 10, 30 min). Thereafter, RBC-NOS Serine1177 phosphorylation was measured utilising immunofluorescence labelling. Shear stress exposure at 0.5, 1.5, and 13.5 Pa significantly increased RBC-NOS Serine1177 phosphorylation following 1 min (p < 0.0001); exposure to 4.5 Pa had no effect after 1 min. RBC-NOS Serine1177 phosphorylation was significantly increased following 10 min at each magnitude of shear stress (0.5, 1.5, 13.5 Pa, p < 0.0001; 4.5 Pa, p = 0.0042). Shear stress exposure for 30 min significantly increased RBC-NOS Serine1177 phosphorylation at 0.5 Pa and 13.5 Pa (p < 0.0001). We found that RBC-NOS phosphorylation via shear stress is non-linear and differs for a given magnitude and duration of exposure. This study provides a new understanding of the discrete relation between RBC-NOS and shear stress.

Modified stress and temperature-controlled direct shear apparatus on soil-geosynthetics interfaces

In this paper, a bespoke stress and temperature controlled direct shear apparatus to test soil-geosynthetics interfaces is introduced. By adopting the apparatus, a series of ‘rapid loading’ shear tests and creep tests were conducted on the Clay – Geosynthetic Drainage layer (GDL) interfaces to assess the functionality of the apparatus. The experimental results indicate that, the modified apparatus can allow the shear deformation behaviour of soil-geosynthetics interfaces under environmental stress during thermal and drying-wetting cycles to be investigated, with a reliable performance. The resistance of Clay-GDL interfaces to shear deformation under the rapid loading of shear stress decreases after drying-wetting cycle and at elevated temperature. In the creep tests, the interfaces subjected to drying-wetting cycles and thermal cycles fail under a lower shear stress level than that of the interfaces without experiencing drying-wetting cycles and thermal cycles, respectively. The impacts of drying cycles on the horizontal displacement is significantly larger than that of wetting cycles. The first drying cycle has the largest impacts on the horizontal displacement than those of the following drying cycles. The impacts of drying alone on the horizontal displacement of Clay-GDL interfaces during drying cycles are small, and the main influence factor is the elevated temperature.

Novel in vitro microfluidic platform for osteocyte mechanotransduction studies.

Osteocytes are the major mechanosensing cells in bone remodeling. Current in vitro bone mechanotransduction research use macroscale devices such as flow chambers; however, in vitro microfluidic devices provide an optimal tool to better understand this biological process with its flexible design, physiologically relevant dimensions and high-throughput capabilities. This project aims to design and fabricate a multi-shear stress, co-culture platform to study the interaction between osteocytes and other bone cells under varying flow conditions. Standard microfluidic design utilizing changing geometric parameters is used to induce different flow rates that are directly proportional to the levels of shear stress, with devices fabricated from standard polydimethylsiloxane (PDMS)-based softlithography processes. Each osteocyte channel (OCY) is connected to an adjacent osteoclast channel (OC) by 20-μm perfusion channels for cellular signaling molecule transport. Significant differences in RANKL levels are observed between channels with different shear stress levels, and we observed that pre-osteoclast differentiation was directly affected by adjacent flow-stimulated osteocytes. Significant decrease in the number of differentiating osteoclasts is observed in the OC channel adjacent to the 2-Pa shear stress OCY channel, while differentiation adjacent to the 0.5-Pa shear stress OCY channel is unaffected compared with no-flow controls. Addition of zoledronic acid showed a significant decrease in osteoclast differentiation, compounding to effect instigated by increasing fluid shear stress. Using this platform, we are able to mimic the interaction between osteocytes and osteoclasts in vitro under physiologically relevant bone interstitial fluid flow shear stress. Our novel microfluidic co-culture platform provides an optimal tool for bone cell mechanistic studies and provides a platform for the discovery of potential drug targets for clinical treatments of bone-related diseases.

Granule attrition by coupled particle impact and shearing

A novel device has been developed for continuous shearing and repeated impact of granules in order to simulate granule attrition and dust formation under realistic plant conditions of mechanical stresses, shear strains and strain rates. The device subjects the granules to multiple impacts at a range of velocities prevailing in typical process plants, and to shear deformations using two rollers with an adjustable gap to simulate the level of shear stresses and strains experienced during bulk motion, e.g. discharge from silos onto conveyor belts, etc. In this paper, the device operation and tests carried out to determine the settings required for attaining a desired impact velocity and shear strain rate are described. Subsequently, the extent of breakage of the granules is determined for the specified settings and the results are compared with data obtained by more established methods, e.g. annular shear cell and single particle impact tests.

Piezo1 channels mediate trabecular meshwork mechanotransduction and promote aqueous fluid outflow.

Trabecular meshwork (TM) is a highly mechanosensitive tissue in the eye that regulates intraocular pressure through the control of aqueous humour drainage. Its dysfunction underlies the progression of glaucoma but neither the mechanisms through which TM cells sense pressure nor their role in aqueous humour outflow are understood at the molecular level. We identified the Piezo1 channel as a key TM transducer of tensile stretch, shear flow and pressure. Its activation resulted in intracellular signals that altered organization of the cytoskeleton and cell-extracellular matrix contacts and modulated the trabecular component of aqueous outflow whereas another channel, TRPV4, mediated a delayed mechanoresponse. This study helps elucidate basic mechanotransduction properties that may contribute to intraocular pressure regulation in the vertebrate eye. Chronic elevations in intraocular pressure (IOP) can cause blindness by compromising the function of trabecular meshwork (TM) cells in the anterior eye, but how these cells sense and transduce pressure stimuli is poorly understood. Here, we demonstrate functional expression of two mechanically activated channels in human TM cells. Pressure-induced cell stretch evoked a rapid increase in transmembrane current that was inhibited by antagonists of the mechanogated channel Piezo1, Ruthenium Red and GsMTx4, and attenuated in Piezo1-deficient cells. The majority of TM cells exhibited a delayed stretch-activated current that was mediated independently of Piezo1 by TRPV4 (transient receptor potential cation channel, subfamily V, member 4) channels. Piezo1 functions as the principal TM transducer of physiological levels of shear stress, with both shear and the Piezo1 agonist Yoda1 increasing the number of focal cell-matrix contacts. Analysis of TM-dependent fluid drainage from the anterior eye showed significant inhibition by GsMTx4. Collectively, these results suggest that TM mechanosensitivity utilizes kinetically, regulatory and functionally distinct pressure transducers to inform the cells about force-sensing contexts. Piezo1-dependent control of shear flow sensing, calcium homeostasis, cytoskeletal dynamics and pressure-dependent outflow suggests potential for a novel therapeutic target in treating glaucoma.

Earthquake Rupture Through a Step‐Over Fault System: An Exploratory Numerical Study of the Leech River Fault, Southern Vancouver Island

AbstractThe Leech River fault (LRF) zone located on southern Vancouver Island is a major regional seismic source. We investigate potential interactions between earthquake ruptures on the LRF and the neighboring Southern Whidbey Island fault (SWIF), which can be interpreted as a step‐over fault system. Using a linear slip‐weakening frictional law, we perform 3‐D finite‐element simulations to study rupture jumping scenarios from the LRF (source fault) to the SWIF (receiver fault), focusing on the influences of the offset distance, fault initial stress level, and fault burial depth. We find a smaller offset distance, a higher initial stress level on either fault, or a shallower fault burial depth will promote rupture jumping. Jumping scenarios can be interpreted as the response of the receiver fault to stress perturbations radiated from the source fault rupture. We demonstrate that the final rupture jumping scenario depends on various parameters, which can be collectively quantified by two keystone variables, the time‐averaged over‐stressed zone (where shear stress exceeds static frictional strength on the receiver fault) size and the receiver fault initial stress level. Specifically, a smaller offset distance, a higher initial shear stress level, or a shallower burial depth will lead to a larger . The seismic moment on the receiver fault increases with increasing . When reaches the threshold dependent on the receiver fault initial stress level, the rupture becomes breakaway.

Lymph Node Subcapsular Sinus Microenvironment-On-A-ChipModeling Shear Flow Relevant to Lymphatic Metastasis and Immune Cell Homing.

SummaryA lymph node sinus-on-a-chip adhesion microfluidic platform that recapitulates the hydrodynamic microenvironment of the lymph node subcapsular sinus was engineered. This device was used to interrogate the effects of lymph node remodeling on cellular adhesion in fluid flow relevant to lymphatic metastasis. Wall shear stress levels analytically estimated and modeled after quiescent and diseased/inflamed lymph nodes were experimentally recapitulated using a flow-based microfluidic perfusion system to assess the effects of physiological flow fields on human metastatic cancer cell adhesion. Results suggest that both altered fluid flow profiles and presentation of adhesive ligands, which are predicted to manifest within the lymph node subcapsular sinus as a result of inflammation-induced remodeling, and the presence of lymph-borne monocytic cells may synergistically contribute to the dynamic extent of cell adhesion in flow relevant to lymph node invasion by cancer and monocytic immune cells during lymphatic metastasis.

Mechanosensitive Notch-Dll4 and Klf2-Wnt9 Signaling Pathways Intersect in Guiding Valvulogenesis in Zebrafish

In the zebrafish embryo, the onset of blood flow generates fluid shear stress on endocardial cells, which are specialized endothelial cells that line the interior of the heart. This mechanical stimulation activates signaling pathways that play crucial roles in atrioventricular valvulogenesis. High levels of fluid shear stress activate both Notch and Klf2 signaling in endocardial cells, causing some to ingress into the cardiac jelly and initiate valvulogenesis. But it remains unclear why only specific, individual cells respond this way, and how the mechanosensitive Notch and Klf2 pathways contribute to the process. Here, we show that lateral inhibition between endocardial cells, mediated by Notch, singles out Delta-like 4-positive endocardial cells. These cells ingress into the cardiac jelly where they form an abluminal cell population. High Notch activity prevents this cell behavior. We also find that Delta-like 4-positive cells only ingress in response to Wnt9a, which is produced in parallel through an Erk5-Klf2-Wnt9a signaling cascade also activated by blood flow. Our work explains how mechanical stimulation activates parallel mechanosensitive signaling pathways that cooperate and produce binary effects by driving endocardial cells towards either luminal or abluminal fates. Ultimately, these cell fate decisions sculpt cardiac valve leaflets.

Fluid Shear Stress Induces EMT of Circulating Tumor Cells via JNK Signaling in Favor of Their Survival during Hematogenous Dissemination.

Tumor cells metastasize to distal organs mainly through hematogenous dissemination, where they experience considerable levels of fluid shear stress. Epithelial–mesenchymal transition (EMT) plays a critical role in tumor metastasis. However, how fluid shear stress influences the EMT phenotype of circulating tumor cells (CTCs) in suspension has not been fully understood. The role of shear-induced EMT in cell survival under blood shear flow remains unclear. This study shows that the majority of breast CTCs underwent apoptosis under shear flow and the surviving cells exhibited mesenchymal phenotype, suggesting that fluid shear stress induces EMT. Mechanistically, fluid shear stress-activated Jun N-terminal kinase (JNK) signaling, inhibition/activation of which suppressed/promoted the EMT phenotype. In particular, shear flow facilitated the JNK-dependent transition of epithelial CTCs into the mesenchymal status and maintained the pre-existing mesenchymal cells. Importantly, the induction of EMT suppressed the pro-apoptosis gene p53 upregulated modulator of apoptosis (PUMA) and enhanced the survival of suspended CTCs in fluid shear stress, which was rescued by overexpressing PUMA or silencing JNK signaling, suggesting that shear-induced EMT promotes CTC survival through PUMA downregulation and JNK activation. Further, the expressions of EMT markers and JUN were correlated with poor patient survival. In summary, our findings have demonstrated that fluid shear stress induces EMT in suspended CTCs via JNK signaling that promotes their survival in shear flow. This study thus unveils a new role of blood shear stress in CTC survival and facilitates the development of novel therapeutics against tumor metastasis.

Gambusia holbrooki Survive Shear Stress, Pressurization and Avoid Blade Strike in a Simulated Pumped Hydroelectric Scheme

Pumped hydroelectric energy storage (PHES) projects are being considered worldwide to achieve renewable energy targets and to stabilize baseload energy supply from intermittent renewable energy sources. Unlike conventional hydroelectric systems that only pass water downstream, a feature of PHES schemes is that they rely on bi-directional water flow. In some cases, this flow can be across different waterbodies or catchments, posing a risk of inadvertently expanding the range of aquatic biota such as fish. The risk of this happening depends on the likelihood of survival of individuals, which remains poorly understood for turbines that are pumping rather than generating. This study quantified the survival of a globally widespread and invasive poeciliid fish, Eastern gambusia (Gambusia holbrooki), when exposed to three hydraulic stresses characteristic of those experienced through a PHES during the pumping phase. A shear flume and hyperbaric chamber were used to expose fish to different strain rates and rapid and sustained pressurization, respectively. Blade strike models were also used to predict fish survival through a Francis dual turbine / pump. Simulated ranges were based on design and operational conditions provided for a PHES scheme proposed in south-eastern Australia. All gambusia tested survived high levels of shear stress (up to 1853 s-1), extremely high pressurization (up to 7600 kPa gauge pressure) and the majority (> 93 %) were unlikely to be struck by a turbine blade. Given their tolerance to these extreme simulated stresses, we conclude that gambusia will likely survive passage through the simulated PHES scheme if they are entrained at the intake. Therefore, where a new PHES project poses the risk of inadvertently expanding the range of gambusia or similar poeciliid species, measures to minimize their spread or mitigate their ecosystem impacts should be considered.